Try to practice from the Manhattan Tests, they are tad tougher than the GMAT. What is your current GMAT Quant score. I have found that for almost all students, the approach to the questions matters more than the solving more questions.

hmm. I would recommend to focus on approach and solve questions with clock time of 1 min 50 sec. This would help you get aware clock pressure. It would be helpful to use Grockit Subscription to practice quant.